Abhijit V. Banerjee said this quote

the parts of the brain corresponding to the limbic system (thought to respond only to more visceral, immediate rewards) were activated only when the decision involved comparing a reward today with one in the future. In contrast, the lateral prefrontal cortex (a more “calculating” part of the brain) responded with a similar intensity to all decisions, regardless of the timing of the options. Brains that work like this would produce a lot of failed good intentions. And indeed, we do see a lot of those, from New Year’s resolutions to gym memberships that lie unused.